Here are two related problems I was thinking about and wonder if you can chime in (didn't see any related threads on these issues already): 1. Say there is a galactic "community" made-up of various species of sentient beings (humans being one of them). Say they have a central meeting place where political affairs are discussed, treaties are signed, etc. The question is this: Would such an arrangement require a sort of universal time-keeping standard? I.e. how would the humans arrange a meeting with aliens on the other side of the galaxy? Of course they wouldn't say, "Ok, let's meet at point X on Wednesday at 5:00pm" since outside of Earth the 24 hour clock and Gregorian calendar are completely meaningless, and probably other reasons you guys know about that I do not. This is a big problem I have run into and I don't even know if I'm thinking of it in the right terms. I would think that a galactic community that has to arrange meetings and schedule things would have some sort of universal, objective standard of time and date that could be easily referenced. Any one have any ideas or thoughts on this? 2. Say there are a number of human colonies located on various exoplanets separated by tens of thousands of light years. Forgetting how they actually got there in the first place, let's say they have some sort of central government (in addition to their planetary, national, local governments, etc.) What ways might a civilization like this maintain an objective calendar-keeping system? I assume that if whatever the capital world of such a civilization would create a new calendar based on the orbital period of their own star, but would do you think this would be absolutely necessary?